1. Field of the Invention
The present application relates in general to helicopter acoustics, in particular, to the reduction of a helicopter acoustic signature.
2. Description of Related Art
Efforts to curtail the sound produced by aircraft, such as helicopters, has been a focus for many years. Helicopters produce sound from the engine and transmission as well as sound from compression waves generated by the passing of each rotor blade.
Efforts to address the sound of helicopters have typically been in one of two areas. First, efforts regarding noise cancellation have been directed to the cabin of the helicopter. This would typically involve the use of sound deadening materials and insulation layers. Such efforts generally look to insulate cabin passengers from rotor blade noise rather than reducing helicopter acoustic signature.
Secondly, efforts have been made in the area of helicopter noise reduction. Noise reduction has typically come via advancements in blade design by minimizing main or tail rotor tip speed, for example. Other efforts have included ducted tail rotors or other blade symmetry alterations. These particular techniques often require overall design changes to rotor geometry, power, avionics, and transmission, and generally cannot be made after the helicopter has completed production. Also, such efforts are primarily concerned with noise reduction rather than noise cancellation.
None of these methods or efforts fully addresses cancellation of the acoustic signature of a helicopter, therefore considerable shortcomings remain.
While the system and method of the present application is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the application to the particular embodiment disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the process of the present application as defined by the appended claims.